In the empirical model developed by Y. Shimomura [1], it is assumed that plasma makes a transition from L-mode to H-mode when the power crossing the separatrix () rises above a power threshold ():

The power threshold for the transition to H-mode is calculated using the following formula,

where *A*_{H} is the hydrogenic mass in AMU, is the vacuum
toroidal magnetic field at major radius *R* along the flux surface in
Tesla, *R* is the major radius in meters, is the line
average density in units of 10^{20} m^{-3} and *a* is the minor radius in meters. The RMS deviation of this model is 27%.

Wed Apr 2 12:00:26 EST 2003